1. Field of the Invention
The invention relates to the production of ceramic oxide flakes, and in particular, the preparation of ceramic oxide flakes using a foam reactor.
2. Discussion of Background
The economical production of ceramic oxide flakes is of continuing industrial importance. Ceramic oxide flakes may be used for preparing ceramic coatings on substrates as well as for producing coating pigments. Flakes or high aspect ratio powders or particles when coated on a substrate offer high surface coverage, and therefore substantially reduce the amount of material required to coat a given surface. Alumina and titania have potential applications in pigments and coatings while zirconia flakes can be used in preparing more uniform electronic and magnetic tapes and devices.
A further use of ceramic flakes is the reinforcement of ceramic matrices. Conventional research in the reinforcement of ceramic matrices has focused on fibers and whiskers. However, the one dimensional nature of fibers and whiskers poses distinct limitations on their use in components requiring multidirectional strength properties. Flakes, therefore, have the potential for developing reinforced composites with optimum optical, mechanical and thermal properties in two dimensions. For example, to achieve planar reinforcement with fibers or whiskers requires the use of multiple crossplies which results in approximately 60% reduction in mechanical properties in any one direction. With flakes, it is possible to achieve planar reinforcement directly, since they display planar isotropic characteristics. Bimetallic flakes have been used to reinforce metals such as aluminum (see Hertzberg, R. W. "Potential of Unidirectionally Solidified Eutectic Alloys as Reinforced Composites", Fiber Composite Materials, ASM, p. 77 (1965) and glass flakes have been found to improve the Young's modulus and flexural strength of composite materials (see Oleesky, S. and Mohr, G. Handbook of Reinforced Plastics, Reinhold, p. 148 (1964).
Several processes for preparing glass, metal and ceramic flakes are known. For example, U.S. Pat. No. 3,066,065 discloses a process for preparing glass flakes by drawing molten glass into an extremely thin sheet from which the glass flakes are produced. U.S. Pat. No. 3,340,006 discloses a method for producing flakes of a metal oxide, such as oxides of titanium, indium, tantalum, zirconium and tin. Additionally, U.S. Pat. No. 3,888,687 and SU-408,937 disclose compositions containing ceramic oxide flakes.
A continuing need exists, however, for new economical and convenient methods of preparing ceramic oxide flakes. The present invention is directed to such a novel process which utilizes the unique characteristics of foams in the production of ceramic oxide flakes.
Foams are coarse dispersions of gas in a relatively small amount of liquid. Foams have been studied scientifically with regard to the behavior of liquid films and have been used in a wide variety of consumer and industrial applications. For example, foams have found particular application in shampoos, shaving creams, and other consumer compositions which require long-lived foams. Foams have also found applications in the area of froth floatation, e.g., in the separation of mineral materials, fire extinguishing foams, foam fractionation and petroleum operations, for example, in drilling operations.
Applicant has now discovered an economical and efficient process for the production of ceramic oxide flakes using a foam reactor. The process of the present invention produces ceamic oxide flakes having consistent particle sizes and enables control of the relative particle size of the ceramic oxide flakes.